The Kid Thief
by TMan5636
Summary: Ferb is injured, Grim's Scythe is stolen, Trixie Tang is on the run, The Eds get a mysterious book, Dib investigates a murder and there's a kid thief on the loose. A crossover of five in one massive story full of mysteries and diamonds. Read and find out. Rated T.


_**The Kid Thief!**_

Chapter 1: Brotherly Bond

September 12th - 11:34am - Danville

There was a calm autumn breeze throughout the suburban areas of Danville, we find Isabella riding her bike straight into the wind making her way to the Flynn-Fletcher residence, for no real reason apart from to see the boy of her dreams, Phineas.

The house was in her sights, she felt a little excited, but also concerned. She always enjoyed watching Phineas be himself, but as of late, things have been rather bland at the place to say the least. For the past few weeks, almost nothing has been done, no crazy inventions, no wild adventures, nothing. She even heard a rumour that Phineas and his step brother Ferb has been drifting apart, to her this seems unbelievable, the two have had an incredibly strong bond since they were babies.

Isabella made it to the house and chained her bike where the other bikes were kept, she walked into the back garden where Phineas and Ferb would often be found making their wild inventions, but today, it was empty, no sign of either of them, nor any machines or tools out in the open. It was the same as yesterday, and the day before. She was hoping to have seen them do something, that this whole unusual situation had resolved.

She knocked on the back door and slowly opened it, there she was met with their mother. "Oh hi Isabella." she said. "Phineas is in his room."

"Thank you." She said pulling a sweet smile, trying to hide her concern. She then made her way to Phineas and Ferb's bedroom. She made her way to the upstairs hallway and found the door to their room. She felt almost afraid to see what was going on, but she opened it anyway.

Upon opening the door, she found the two beds. She saw that Phineas was sitting on his bed playing video games with a bored look on his face, Ferb on the other hand was nowhere in sight. This sighting felt so unnatural to her.

Phineas moved his eyes slightly to see Isabella, he became really surprised. "Oh, hey Isabella!" he said suddenly gaining his energy back, he quickly turned the game off and walked up to her. Isabella was glad to see his smile again, but was confused on seeing him change moods so quickly.

"Hey Phineas, I came to see how you were, I'd ask what'cha doing but... I could already tell."

Phineas turned to his console with a faint chuckle, then faced her again. "Heh, yeah. Yeah I was a little bored so I thought I'd do a bit of catching up on my old games, they were collecting quite a bit of dust."

"Hm, so how come you're not building anything? And where's Ferb?"

Phineas suddenly lost his smile. "I... well it's kind of difficult to build a lot of things without Ferb, and he left the house a couple hours ago."

"Really? Any idea where he went?"

"No, he just said he's going out. I'm sure whatever he's doing, I'm sure it's important."

Isabella felt hesitant to ask, but she had to say something, she needed to know. "Phineas...? Have you and Ferb... been falling apart?"

Phineas looked a bit surprised, he then sighed. "Couldn't hide it from you, could I?"

"So, you two have been having a disagreement?"

"It's not a disagreement per say." Phineas rubbed the back of his neck a bit. "For the past few weeks, Ferb's been kind of... drifting away. Every day it was almost the same thing, he would leave the house very early, come back very late, even during school, he would leave during lunch to go on the computers in the library. He's been doing that for so long, I kinda feel that he's... I kind of feel that he's trying to keep away from me."

Isabella could feel the pain Phineas was feeling, to have his brother whom he couldn't be closer with, just suddenly start to drift away so quickly. Isabella gently placed her hand on Phineas' shoulder. "Look, I'm sure he still loves you as a brother, he might just need to do something important like you said."

Phineas pulled a smile. "T-Thanks."

Isabella could tell it was a forced smile. "Look, why don't we build something together? I may not know a lot about machines compared to Ferb, but I can still help you, right?"

She soon saw Phineas pulling a real smile. "Yeah! Isabella, I know what we're going to do today!" The two then made their way out of the room and towards the garden. Isabella felt incredibly pleased to see Phineas really happy again, but she was still concerned with what Ferb was doing. She wanted to find out, but right now keeping Phineas happy was top priority.

* * *

><p>Throughout the rest of the day, Phineas and Isabella had built at least three different large fun-loving machines to spend the day with. Isabella suspected that Phineas wanted to build so much because he hadn't gotten to do it for so long, he had a similar moment when they climbed a mountain with Baljeet and they never used a single contraption.<p>

It was now at least six in the afternoon and we find the two sitting on the couch together feeling quite tired, Isabella was glad she got Phineas' energy back in making the most of each day, but she was still worried about Ferb. He still hasn't came home yet.

The two began to watch TV for a little while, deciding to take it easy for the rest of the day. Isabella phoned her mother and asked if she could sleep over, and she was. She looked over to Phineas who had his pet Platypus Perry sleeping on his lap, while he was smiling all the same, she felt it was only a matter of time before he is reminded of Ferb and becomes worried again, Isabella couldn't stop this, but she knew she had to comfort him at least.

"We interrupt this broadcast for an important news bulletin." Phineas, Perry and Isabella felt a bit surprised seeing this.

"Not one hour ago after the Danville Museum had closed, a member of the public had hidden himself in the museum and had stolen a rare piece of jewellery that had not long been donated."

Several camera shots appeared showing the shadowed figure around the museum. While it was difficult to tell how it was, there were two major points, one was that the figure was short, so a possible child. The other was that he had an F shaped head and a bit of fuzzy hair.

"FERB!?" both of them exclaimed as Perry's jaw dropped.

"While the police haven't identified the thief in question, the thief seemed to have a lot of knowledge on the museum's diagrams and level of security if he was able to steal a small diamond. Although we are unsure of the motive of the crime, there are hundreds of other more valuable artefacts and gemstones in the museum, which begs the question of why the thief only stole their most recent exhibit."

The two couldn't be in more shock, that was Ferb no doubt, and the fact that he had been secretly going off to do his own thing now for weeks only proved he used that time to break into the museum. But neither of them could understand why.

Isabella turned to Phineas' horrified face, she had no idea what to say or how to comfort him, this all felt like he was just stabbed in the back.

But before Isabella could say anything, Phineas placed Perry back on the couch and suddenly made his way to the front door. "Phineas, wait!" Isabella suddenly got up herself and ran after him. Just before Phineas could open the door, Isabella grabbed his other arm. "Hold on! Where are you going?"

"I have to find Ferb, I don't believe this for even a second!"

"And where are you going to find him?"

"I... I don't know. But he has to be somewhere."

Isabella could feel his sadness and anger, she knew that nothing would convince him to stay put and just wait for him to return. "Look, I'm going with you." Phineas looked a bit surprised. "I know I can't convince you to stay, so let me come with you at least."

Phineas was silent at first, but he then nodded. "Alright, let's go find Ferb."

* * *

><p>The sun was setting fast, with only a couple of hours of daylight left, Phineas and Isabella rode on their bikes all across Danville, they asked as many people as they could if he saw Ferb, but sadly to no avail. Isabella was feeling more and more worried of the situation, not only was this completely out of character for Ferb, but she could sense just how much in pain Phineas was. She never had any siblings so she can't tell how it must feel, but she knows it must be bad.<p>

Phineas looked from right to left constantly, looking more worried. "FERB! WHERE ARE YOU!?" he shouted.

Isabella looked ahead to see it was getting darker, she looked around to see there were less people. An ominous vibe coursed itself through her, she's never been in the city this late. She slowly turned to Phineas.

"Phineas, listen." Phineas turned to her. "It's getting late... maybe we should head back."

"What? But-"

"I know you're worried, I don't know what it's like to have a brother or sister do this considering I'm an only child. But we can't find Ferb in the dark."

Phineas looked over to the setting sun. "Yeah, I think we might be able to build something that can brighten up the entire city for us."

"Phineas I-"

"Or maybe something to keep the sun and moon in place just until we find Ferb."

"Phineas-"

"Wait! We could build a tracking device to find Ferb, I'm sure he has some bits of hair in our room-"

"PHINEAS!"

Phineas jumped at Isabella's tone as he turned to her again, she looked somewhat angry, but then changed back to looking concerned. She placed her hand on Phineas' shoulder. "I'm saying that we should head home and wait for Ferb there."

"B-But-"

"He has to come home sooner or later, who knows. He might already be home right now. It's getting late, we should just wait for him."

Phineas looked around quite a bit hoping to come up with a good reason to stay, but he eventually sighed and faced Isabella again. "A-Alright, let's head home."

Just before either of them could turn and move their bikes, they heard the sound of running footsteps coming from above. They both looked up and to their left where the sound was coming from, there they saw a shadow running on top of the buildings, it was difficult to see who it was at first, but this shadow soon held up a large pole as it ran and pole vaulted across to the next building, this shadow had an F shaped head.

"FERB!?" both of them exclaimed.

"Quick! We gotta get to him!" Phineas exclaimed as he quickly turned his bike around and peddled as fast as he could. Isabella shortly caught up with him and they began to chase after Ferb who continued to run along the top of the buildings.

Ten minutes passed and we find Ferb in a black full body suit who stopped running for a moment to catch his breath, he quickly looked all around him feeling a sense of dread within him. He soon calmed down. "Lost him." he muttered under his breath.

"Ferb!"

He jumped a bit and turned to his right to see Phineas arriving onto the roof via a ladder, Isabella not long followed. "Phineas!?" he exclaimed.

"Ferb! What the heck are you doing!?" exclaimed Phineas.

"Didn't you know how much you were making your brother worried!?" exclaimed Isabella.

"Look, I'm sorry but now's not the time!" said Ferb as he looked around.

"No! Now's the perfect time!" said Phineas sounding assertive. "Why have you been leaving for so long so often!? And please tell me you weren't the one who robbed the museum!?"

"Listen Phineas, I know I have a lot to explain, but now is really bad. I'm-"

_"Going to surrender that diamond or else!" _said a fourth voice.

The three looked around feeling worried, trying to find the source of the voice. They suddenly heard a loud banging sound from the right, they looked to see that there was someone else on top of the roof's door.

It was a boy roughly their age, he had insane looking brown spiky hair and blue eyes. He wore a navy blue long shirt with a thick grey scarf around his neck which covered his mouth, a black eye mask, tight navy blue trousers and shoes, he wore very thick brown gloves with pointed blades on each finger tip acting like claws, and he oddly enough, had a black tail with a white tip that swishes slowly.

Phineas and Isabella slowly stepped back. "W-Who's that!?" exclaimed Isabella.

This boy chuckled. "You seriously thought you lost me, I merely kept myself hidden so you'd drop your guard." He placed his hand forward showing off his claws. "Now look, I'm on a tight schedule. Give me that diamond!"

"Diamond!?" Phineas turned to Ferb. "Y-You... you DID steal that diamond!?"

Ferb looked to Phineas, and then back to the boy, Ferb then pulled out a metal stick from his pocket, tapped it and it suddenly changed into a large metal pole. "Phineas, Isabella... get out of here now, this kid is really tough."

"What!? N-No I can't!" exclaimed Phineas.

Suddenly the boy jumped up high and landed straight in between both Phineas and Ferb forcing them to stumble back. Ferb immediately reacted by swinging the pole down onto the boy, but he suddenly caught it with one hand and pushed him back.

Phineas and Isabella stepped back in fear and confusion. This boy glared at the nervous Ferb, turned to face Phineas, then back to Ferb. "So... friends of yours?" the boy suddenly placed his hand right in front of Phineas keeping the claws very close to his nervous face. "Give me that diamond. Or else he gets it!"

Ferb suddenly turned nervous to angry. "Y-You leave my brother out of this! This is between you and me!"

"Your brother?" The boy turned to Phineas, then back to him. "Not a lot of resemblance. Look, personally I'd rather make it just you and me, but I need that diamond and you're being uncooperative. Give me it and your brother doesn't get hurt."

Ferb grunted in frustration, but he soon calmed down and dug into his pocket. He pulled out what Phineas didn't want to see, it was a diamond almost the same size as his palm, it had a lovely shine to it and was shaped like a love heart.

Though the boy's mouth was covered, he gave signs of a smirk. "I gotta hand it to you, getting that diamond before I arrived. You clearly did your research on that museum very well. You'd make a good thief, but I make a much better one."

"Thief?" muttered Isabella. "This boy is a thief?"

Ferb slowly stepped forward and placed his hand out holding the diamond. The boy lifted his free hand up to accept it. Just as the boy was about to take it, Ferb suddenly threw it high into the air, the boy looked up surprised, then looked straight ahead seeing Ferb swinging the pole to his head.

The boy ducked lightning fast with only the pole being an inch away from hitting him, Ferb swung again a bit lower but the boy jumped up with a back flip. Ferb then swung vertically but the boy jumped to the side dodging it easily.

The boy looked at the diamond still in the air and he jumps for it, the boy catches it in mid air and lands near the edge of the building, looking like he was ready to jump off. But Ferb suddenly grabbed the boy's tail making him grunt in pain, Phineas and Isabella became shocked to see that the tail was real.

Ferb pulled him back onto the building making him stumble as Ferb tried to hammer him with the pole, but the boy suddenly threw a kick into his chest sending him back a bit. The boy then threw three more kicks but Ferb blocked all of them the pole, Ferb then swung his pole forward but the boy dodged.

Just before the boy could do anything else, Phineas suddenly grabbed his tail and pulled hard. The boy growled in anger and pain.

"No Phineas! Don't!" shouted Ferb.

The boy suddenly shot around forcing Phineas to lose his grip, the boy then jumped and done a spinning kick right into Phineas' face sending him far back and hitting the ground hard. Isabella gasped right before running to him.

Ferb swung his pole again but the boy quickly caught it and tried to pull it off of him. Ferb and the boy began pulling at the pole back and forth, until Ferb pulled even harder tipping his head back, he then swung his head into the boy's throwing him off of the pole. As the boy stumbled, Ferb quickly pried the diamond out of his gloved hand.

The boy swiped at him with his claws but Ferb dodged just in time. He swung the pole down again but the boy dodged, slammed his foot down onto it keeping it in place. He then kicked at it with his other foot sending it upwards causing it to smack Ferb in the face, the boy kicked it again sending it flying up. He then kicked Ferb in the stomach sending him further back, the boy then jumped up preparing another spinning kick, striking the pole as it came down sending it flying right towards Ferb.

The pole smacked him sending him flying back and right on the edge of the roof. He was about to fall off but the boy leapt forward and grabbed his arm which grasped the diamond. The boy glared at the angered yet nervous Ferb as he was tipped so far, the boy letting go would make him fall instantly.

"All you had to do was give me the diamond. Is that really so hard?"

Isabella felt horrified to see this, Phineas slowly leaned up regaining consciousness, he saw the scene and felt shocked. "Ferb!"

The boy gently moved his other hand and made an attempt to take the diamond. But Ferb suddenly pulled out a small knife from his pocket and stabbed the arm holding onto him. The boy let out an angered scream of pain as he lost his grip and Ferb began to fall.

"FERB NO!" Phineas screamed as he watched Ferb disappear from sight and the boy held onto his wrist in pain.

Ferb fell far, he smacked his back onto a metal flagpole and rolled off of it, luckily he managed to grab it but he quickly lost his grip and landed on a clothed roof softening his fall, but he quickly rolled off and hit a few trashcans.

Phineas and Isabella ran to the edge to see Ferb, both looked horrified to see this, they looked to the boy who jumped off of the roof and landed on the metal pole with ease, he walked along it and looked down at Ferb. Phineas and Isabella quickly ran back to the ladder to try and get down.

They made it all the way down and ran towards the unconscious Ferb, there they saw the boy gently take the diamond out of his hand. He placed the diamond in a small pouch attacked to his hip. He saw Phineas and Isabella facing him with angered yet nervous looks.

The boy let out a sigh. "I'm behind schedule now thanks to him, I'm not wasting my time on either of you." The boy grabbed a small purple ball from his pocket and threw it onto the ground making a large explosion of purple smoke making the two flinch, as the smoke cleared, the boy was gone.

* * *

><p>September 13th - 7:12am - Danville local hospital<p>

Phineas couldn't find it in himself to say what he truly saw, something made him feel hesitant. He, Isabella, his parents and Candace were all in the same room as Ferb who lied in a bed unconscious. Of course everyone was worried, but Phineas himself felt the most hurt, he watched the entire thing and hardly did anything to help.

Phineas was the only one who sat besides Ferb, the others were listening to the doctor.

"Well we do have some good news, he should recover in a few weeks, it's mostly a fractured spine. He'll have to stay here for the time being, once he does, he'll have to wear a brace for another week or so just to be completely sure."

"Well at least there's that, I just hope he wakes up soon." said their father.

"I just want to know why on earth both boys and Isabella would be out so late, and I really want to know how on earth Ferb got himself hurt." said their mother.

Phineas continued to sit in silence, the feel of guilt almost overwhelmed him. "Ferb..." he muttered. "Why couldn't I help you? Was... was I not strong enough?"

"Urgh... grr."

Phineas opened his eyes in shock and turned to Ferb who was slowly opening his eyes, he tried his best to turn to him. "Ph-Ph... Phineas..."

"Ferb." Phineas gently placed his hand on Ferb's arm.

"L-Losing consciousness... and fast..." Ferb muttered. "I'm... so sorry... I tried to... keep you out of this... to protect you..."

"Protect me?"

"Phineas... that diamond... he stole... you... you've ugh, you've got to get it back."

"But... but why?"

"There are... twelve total... Diamond Hearts... you... you've got to get them... all of them..."

Phineas leaned closer. "I-I don't understand."

"The... diamonds are... not normal... urgh..." Ferb was slowly getting weaker. "Do whatever it takes... get those diamonds... all twelve of them..." he turned back to Phineas. "You can't let them... fall into the wrong hands..."

"The wrong hands?" Phineas felt shocked to see Ferb tip down, losing consciousness once again. "Ferb, wait!" he exclaimed as he held his shoulders. He noticed something, in his other hand was the knife he used to stab the boy, it still had his blood on it.

"So that's it..." Phineas muttered, he gently took the knife out of his hand. He came to the conclusion that, he chose to stab the boy, not so as to defend the diamond, but use it as a method of letting him track him down. Ferb knew if he took the diamond and didn't get a sample of his blood, it would be next to impossible to track him down.

Two hours later, Phineas was back home, he was on the finishing touches to making a portable tracking device.

'_So... Ferb was keeping away from me and studying that museum... just so he could get to that diamond before the thief? Ferb said the diamonds weren't normal, what could he mean by that? And there's twelve of them? And why can't they fall into the wrong hands?_'

Phineas finally finished the tracking device, he lifts it up in front of him to give it a quick examine. After doing so, he looked to his right to see the blood stained knife, he picked it up and placed a sample of the blood into a slot and closed the lid. After a few seconds of beeping from the machine, the screen in the middle suddenly turned on and revealed an arrow going southwest.

"I don't know exactly what's going on, but I'm going to get those diamonds."

* * *

><p>We find Phineas just outside his house, he had a large backpack filled with spare clothes, some food and several gadgets and machine parts just in case, in addition to the blood stained knife in a sealed plastic bag. On the front of his bike was the tracking device in question, as well as headlights and other safety measures. He knew he was going to be gone for a long time, and he knew his family was going to be really worried sick, but he didn't care, all he cared about was fulfilling his brother's wish.<p>

He looked back at his house for a moment, remembering he left a note in his room saying where he was going and what he was doing. He sighed and started peddling forward, hoping he won't get stopped immediately, he turned and left the house, glancing at it one last time before it disappeared from sight as he started to move faster.

Phineas began to cycle down a hill and saw the outskirts of town straight ahead, he glanced at his tracking device to see it was on target, he looked back and gasped in shock. Someone else on their bike was right in his path, completely stopped so as to block him.

Phineas slammed on his brakes and almost lost balance in the process, but he saw that the one who blocked him was Isabella herself.

"Isabella!? What-"

"You're going after him aren't you?"

"I... well yes, Ferb wanted me to get the diamond back?"

"But why?"

"I don't know completely, but he said they can't fall in the wrong hands."

"They? There's more than one of those diamonds?"

"I..." Phineas felt worried, he felt that he was giving out too much information. "Look I don't know the full details, but Ferb wanted me to get that diamond back and get the other eleven ones that are part of it. I'm not going back until I do and I... I can't let you stop me!"

Isabella glared at him for a moment, she then tipped her head directing Phineas to the large backpack on her back. "W-Wait? What?" Phineas muttered.

"You have no idea how far you're going, we've travelled across the world in several machines as a team, and now you're planning on going on your own?" Isabella smirked. "I'm not here to stop you, I'm here to help."

"B-But that thief, he's dangerous."

"That's why you'll need my help, I'm a Fireside Girl and our duty is to help. Plus if you never go anywhere without Ferb, so I'm going to have to take his place for the time being."

Phineas felt worried, he had no way to convince Isabella to stay here where it's safe. He let out a sigh and faced her again. "You're really fixed on doing this aren't you?"

"Yes, I'm going with you whether you want me to or not."

The determination in Isabella's eyes proved to him that she was serious. He wasn't going to like this, but he knew he had no choice. "Alright, let's go." Isabella smiled, she then moved her bike forward again and both of them began to peddle forward.

The two of them soon arrived at the outskirts of Danville. Phineas checked the tracking device to see it was pointing forward, then they continued in that direction. Neither of them knew who that thief was or why those diamonds were important, but as Ferb's wish before falling back asleep, they're more than determined to fulfill his wish.

To be continued

* * *

><p><em>Yeah, although I said I was going to retire from fan-fictions and make Digimon Tamers: Rika's AU, my only one, but this was a story idea I just could not drop and the idea of putting it as a fan-fiction was the best choice in my mind.<em>

_But how this fan-fiction will work is kind of different compared to others, Digimon Tamers: Rika's AU is still top priority, this story will only continue once it receives five positive reviews per chapter. So once this chapter has five positive reviews, I will continued to the next chapter._

_Anyway, I hope you liked this. Digimon Tamers: Rika's AU will continue later on._


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